EP3034565A1 - Electrically conductive nanostructures containing titanium - Google Patents

Abstract

The invention relates to a method for treating a titanium oxide compound, wherein the titanium oxide compound is exposed to at least carbon, nitrogen and / or hydrogen and a temperature between 600 ° C and 1200 ° C. With the invention, an increase in the electrical conductivity of titanium oxide compounds can be achieved.

Description

Field of the invention

The invention relates to a method for treating a titanium oxide compound, a method for producing a nanostructure of a titanium oxide, a method for increasing the electrical conductivity of a nanostructure of a titanium oxide and nanostructures of a titanium oxide.

Background of the invention

Nanostructures having a high surface to mass ratio are useful for interfacial applications, for example, as support for catalyst particles in chemical and electrochemical reaction engineering (in heterogeneous catalysis), as photocatalyst, adsorbent, and the like.

Titanium-containing nanostructures with tube or roller form, in particular nanostructures of titanium oxide or titanate, are of particular interest, since they can be produced in a simple process, the so-called hydrothermal process. In the hydrothermal process, a starting material, e.g. a titanium dioxide powder, heated in alkaline solution such as sodium hydroxide for a certain time. According to widespread opinion, thin films or films that can roll up into nanotubes or nanorollets fail. Nanotubes or nanor rolls produced in this way have a large specific surface area.

For example, the European patent publication EP 0 832 847 B1 Such a nanostructural synthesis, wherein titanium dioxide is doped as a starting material for the nanotube synthesis in the sol-gel method with SiO ₂ to achieve an increased specific surface area.

The European patent EP 1 988 059 B1 discloses a nanotube synthesis method in which titanium dioxide nanotubes are produced in a continuous process based on the hydrothermal process and with which nanotube specific surface areas of from 50 m ² / g to 450 m ² / g can be achieved.

The US patent US 7,645,439 B2 discloses the formation of nanostructures of titanium oxide having a composition TiO _2-x where 0≤x≤1. These nanostructures are synthesized starting from amorphous titanium oxyhydroxide or titania produced in the sol-gel process in anatase or rutile modification. With the nanostructures produced with it, specific surface areas of 100 m ² / g to 400 m ² / g can be achieved.

In addition to the large specific surface, the transport of electrons is of particular interest. Electrically conductive nanotubes and nanorolls show great potential for applications as electrode structures, selective membranes, photocatalytic materials, and the like. However, the inherently low electrical conductivity of titanium dioxide and titanate limits the scope of possible applications of conventional nanotubes and titanium oxide nanotubes.

It is therefore desirable to improve the properties of nanotubes and nano-rolls of titanium oxide compounds, in particular the electrical conductivity, with regard to the abovementioned applications, ie in particular to increase the electrical conductivity. A conventional method for improving the properties of nanotubes and nanorubles of titanium oxide compounds and related structures is to introduce carbon and / or nitrogen into the titanium-containing nanotubes and nanorolls (also referred to as doping with carbon and / or nitrogen) or titanium suboxide phases by thermal or chemical To produce reduction. However, there is the problem that the doping or the production of the titanium suboxide phases conventionally takes place under comparatively high temperatures, which may be accompanied by a reduction of the specific surface of the nanotubes or nanor rolls up to a collapse of the tube or roller structure. In addition, there is the problem that with the conventional methods, the electrical conductivity can be increased only insufficient.

Out ME Neville et al., Journal of Photochemistry and Photobiology A: Chemistry, Vol. 267 (2013), pages 17-24 It is also known to dope titanium dioxide with carbon in a sol-gel process and to use the carbon-doped titanium dioxide as the starting material for nanotube synthesis in the hydrothermal process. For the nanotubes thus obtained, however, no increased conductivity could be detected.

The problem underlying the invention

The object of the invention is to improve the electrical conductivity of titanium oxide compounds, in particular nanostructures of titanium oxide compounds and titanium oxide compounds used as starting material for the nanostructural synthesis, in order to enable the provision of nanostructures, in particular in tube or roller form, which have a high photocatalytic activity and / or have a high conductivity.

Inventive solution

The solution of the stated object is achieved by a method for treating a titanium oxide compound, wherein the titanium oxide compound at least carbon, nitrogen and / or hydrogen and a temperature between 600 ° C and 1200 ° C is exposed.

A titanium oxide compound treated by either of these methods contains the elements carbon, nitrogen and / or hydrogen in an amount sufficient to significantly affect their electrical conductivity as compared to an untreated titanium oxide compound. After treatment, these elements were found to occupy interstitial sites in the titanium oxide crystal lattice, to replace oxygen atoms in the titanium oxide compound and / or in the crystal structure of the titanium oxide compound in titanium carbide structure and / or in the form of a mixed crystal of the TiO ₂ phase and / or the TiO ₂ phase and embedded in the TiC phase. This type of embedding or doping leads to an increased electrical conductivity of the titanium oxide compound in comparison to the untreated titanium oxide compound. A part of said elements may also be in the form of amorphous and / or crystalline inclusions in the Contain titanium oxide compound, or in addition to the titanium oxide compound in amorphous and / or crystalline form, for example as amorphous and / or crystalline particles or as an amorphous and / or crystalline coating of the titanium oxide.

The object of the present invention is further achieved by a method for producing a titanium oxide nanostructure, wherein a titanium oxide compound is treated by the method described above, and the titanium oxide compound thus treated is dispersed in an alkaline solution.

The solution of the object is also achieved by a method for producing a nanostructure of a titanium oxide compound, wherein the titanium oxide is exposed to at least carbon, nitrogen and / or hydrogen and the titanium oxide compound thus treated is dispersed in an alkaline solution.

A tubular or roller nanoscale titanium oxide nanostructure made by either of these methods may contain the elements carbon, nitrogen and / or hydrogen in an amount sufficient to significantly increase their electrical conductivity as compared to a tube or roll nanostructure of an untreated titanium oxide compound to influence. It has been found that these elements are also present in the same crystallographic arrangement after the nanostructural synthesis as after the above-described treatment of the titanium oxide compound, so that the electrical conductivity of the nanostructure synthesized therefrom is also increased compared to a nanostructure of an untreated titanium oxide compound.

The solution of the problem is also achieved by a method for increasing the electrical conductivity of a nanostructure of a titanium oxide, wherein the nanostructure of a gas atmosphere and a temperature between 200 ° C and 700 ° C is exposed, wherein the gas atmosphere, an inert gas and another, at least Containing carbon, nitrogen and / or hydrogen-containing gas, and wherein the volume fraction of the further gas in the gas atmosphere is at least 10 percent by volume.

With this method, the electrical conductivity of a tubular or roller-shaped nanostructure of a titanium oxide compound can be further increased by, as described above, carbon, nitrogen and / or hydrogen atoms in the nanostructure are introduced. This requires a certain minimum temperature. By setting a suitable maximum temperature, it can be ensured that only a very small proportion, preferably substantially none of the tube or roller-shaped nanostructures treated in this way, collapses and thus the largest possible specific surface area is maintained. Alternatively, this method can be used to produce an electrically conductive nanoband by setting a suitable minimum temperature from a tubular or roller-shaped nanostructure of a titanium oxide compound.

The solution of the object is further achieved by a nanostructure of a titanium oxide compound, wherein the nanostructure has a tube or roller form, at least carbon, nitrogen and / or hydrogen containing, wherein the amount of carbon, nitrogen and / or hydrogen at least 2 wt%, based on the total mass of the nanostructure, and has an electrical conductivity at room temperature of at least 10 ^-3 S / cm.

The solution of the problem is also achieved by a nanostructure of a titanium oxide compound, wherein the nanostructure has a tube or roller form, at least carbon, nitrogen and / or hydrogen, wherein the amount of carbon, nitrogen and / or hydrogen at least 2 wt%, based on the total mass of the nanostructure, and has a specific surface area of at least 175 m ² / g.

Such nanostructures are particularly suitable for applications as photocatalytic materials, selective membranes, and the like, due to their electrical conductivity and / or their intrinsically large surface area due to the tube or roller shape.

The solution of the problem is also achieved by a nanostructure of a titanium oxide, wherein the nanostructure has a band shape, at least carbon, nitrogen and / or hydrogen, wherein the amount of carbon, nitrogen and / or hydrogen at least 2% by weight, based on the Total mass of the nanostructure, and has an electrical conductivity at room temperature of at least 10 ^-3 S / cm.

Due to their electrical conductivity, such nanostructures are particularly suitable for applications as electrode structures, as conductor tracks with dimensions in the nanometer range and the like.

Overall, the invention thus makes it possible to increase the electrical conductivity of titanium oxide compound and to provide tube, roll or ribbon nanostructures of a titanium oxide compound which have high photocatalytic activity and / or high conductivity.

For the purposes of the present invention, a titanium oxide compound or a titanium oxide material denotes all compounds or materials containing a titanium oxide, in particular in the solid state of aggregation. In particular, these include titanium suboxides, titanium dioxide, titanium dioxide-containing compounds or materials and titanates, in particular salts and esters of titanic acids.

For the purposes of the invention, a powder refers to a mixture of particles, particles or grains, these in particular having no tube or roller shape. The particles, particles or grains may have a spherical shape or be irregular in shape by comparison. The mean grain size of the powder denotes a mean diameter of the particles, particles or grains determined from a multiplicity of particles, particles or grains. The average diameter may refer to an equivalent diameter, i. a diameter obtained from a property determined on the powder, which would have a spherical particle, a spherical particle or a spherical grain having the same property, for example, a volume equivalent spherical diameter, a surface equivalent spherical diameter or a spherical equivalent spherical diameter.

For the purposes of the present invention, a gaseous atmosphere means the introduction of a sample into an environment which contains a gaseous substance or through which a gaseous substance flows. The gas atmosphere may have one or more gaseous substances (gas mixture). A gaseous substance can be composed of individual atoms of a chemical element (for example He or Ar), molecules of a chemical element (for example N ₂ ) or molecules of different chemical elements (for example C ₂ H ₂ ), and also other chemical elements in Contain a form of contamination. Unless otherwise stated, the degree of purity of Gases according to the present invention, ie the relative volume or relative weight of the individual atoms or molecules of the gas in the total volume or total weight of the gas in question, at least 99%, more preferably at least 99.5%, more preferably at least 99.9% , more preferably at least 99.99% and most preferably at least 99.999%.

For the purposes of the invention, an indication in weight percent (also wt%) denotes the relative mass of a component of a mixture of the total mass of the substance mixture. In the same way, volume percent (also vol%) denotes the relative volume of a component of a gaseous, liquid or solid mixture in the total volume of the mixture, and atomic percent (also at%) the relative atomic number of an atomic species in the total number of atoms of a mixture or the relative number on atoms of an atomic species with a certain property on the total number of atoms of this atomic species contained in the mixture. The expression of a solids content in the context of the invention means the mass fraction of a solid relative to the volume of a liquid containing the solid, and is preferably given in grams per liter (g / l).

For the purposes of the invention, atmospheric pressure means a pressure of 1013 mbar. The term normal pressure means a pressure under standard laboratory conditions, in particular a pressure of 1000 mbar at 25 ° C ambient temperature.

For the purposes of the invention, the term electrical conductivity includes both electronic conduction by electrons and ionic conduction, for example by protons. Unless otherwise stated, the term conductivity refers to electrical conductivity.

For the purposes of the invention, the specific surface of a structure means the entire surface of a structure in relation to the mass of the structure. The specific surface area of a structure can be determined by experimental methods or estimated from the shape and dimensions of the structure. Unless otherwise indicated, specific surface area data in the present invention refers to values measured by BET method using N ₂ physisorption.

Demineralized water referred to in the context of the present invention deionized water (also called demineralized water). The electrical conductivity of demineralized water for the purposes of the present invention at room temperature is at most 5 μS / cm, preferably at most 1 μS / cm, more preferably at most 0.1 μS / cm and most preferably at most 0.055 μS / cm.

In the context of the invention, nanotubes designate a nanostructure with a substantially hollow cylindrical shape. A nano roll denotes a nanostructure that is created by rolling up a thin layer or a film, or several layers of the thin layer or the film, once or several times. Nanotubes and nano rolls in the sense of the invention can be closed at the ends, partially fired or open. A nanostructure in the sense of the invention is a product whose structure has a dimension in the nanometer range in at least one spatial direction, preferably at most 1000 nm, more preferably at most 100 nm, particularly preferably at most 50 nm and most preferably at most 10 nm. For example, a tube with an outer diameter of 10 nm and a length of several microns is a nanostructure in the context of the invention.

For the purposes of the invention, the term room temperature means a temperature of 20 ° C. Unless otherwise indicated, in the present invention, electrical conductivity data refer to room temperature values.

Preferred embodiment of the invention

Advantageous embodiments and developments, which can be used individually or in combination with each other, are the subject of the dependent claims.

Process for treating a titanium oxide compound

In a preferred embodiment of the process of the invention for treating a titanium oxide compound, after exposure to carbon, nitrogen and / or hydrogen to the elements, the titanium oxide compound contains at least 2% by weight of carbon, nitrogen and / or hydrogen Total mass of the titanium oxide compound, preferably of at least 4% by weight, more preferably of at least 6% by weight, particularly preferably of at least 10% by weight and most preferably of at least 15% by weight. It is next preferred to indicate the amount of said elements alternatively in atomic percent. In this case, the titanium oxide compound, after being exposed to the elements of carbon, nitrogen and / or hydrogen, contains at least 2 at% of carbon, nitrogen and / or hydrogen, based on the total number of atoms of the titanium oxide compound at least 5 at%, more preferably at least 10 at%, more preferably at least 20 at% and most preferably at least 30 at%. Moreover, after the titanium oxide compound has been exposed to carbon, nitrogen and / or hydrogen to the elements, said elements may not only be contained in the titanium oxide compound itself, but also be present next to and surround the titanium oxide compound, for example in the form of amorphous and / or crystalline ones Particles of said elements or in the form of an amorphous and / or crystalline, complete or partial coating of the titanium oxide compound. The proportion by weight of said elements, based on the total mass of the titanium oxide compound and the elements surrounding the titanium oxide compound as described above, is preferably at least 15% by weight, more preferably at least 20% by weight, more preferably at least 25% by weight, more preferably at least 30% by weight. , more preferably at least 35% by weight, and most preferably at least 40% by weight.

In a further preferred embodiment of the method for treating a titanium oxide compound, the titanium oxide compound is exposed to a gas atmosphere containing at least carbon, nitrogen and / or hydrogen at a temperature between 600 ° C and 1200 ° C. As a result, the elements carbon, nitrogen and / or hydrogen can particularly efficiently take up interstitial sites in the titanium oxide crystal lattice, replace oxygen atoms in the titanium oxide compound and / or in the crystal structure of the titanium oxide compound in titanium carbide structure and / or as mixed crystals of the TiO ₂ phase and / or the TiO ₂ phase and the TiC phase. Preferably, the gas atmosphere contains an inert gas and another, at least carbon, nitrogen and / or hydrogen-containing gas, wherein preferably the volume fraction of the further gas to the gas atmosphere is at least 10 percent by volume. By adjusting the mixing ratio and / or the amount ratio of the inert gas compared to the other gas, the properties of the titanium oxide compound can be selectively changed, in particular by adjusting the volume fraction of the other gas in the gas atmosphere. By a combination of at least two elements of carbon, nitrogen and hydrogen, a Codoping of the titanium oxide compound can be achieved. Preferably, the further gas contains molecules of carbon, nitrogen and / or hydrogen, or carbon, nitrogen and / or hydrogen-containing molecules, wherein a purity of the gas with respect to the molecules is at least 99% by volume, more preferably at least 99.5% by volume. , more preferably at least 99.9% by volume, more preferably at least 99.99% by volume and most preferably at least 99.999% by volume. Preferably, the inert gas is N ₂ and the further gas Ethingas, wherein preferably the volume fraction of the Ethingases in the gas atmosphere is at least 10 percent by volume. By using carbonaceous gases such as Ethingas, it is possible, for example, TiO _x C _y phases with 0 ≤ x <2 and 0 <y ≤ 0.05 and / or mixed crystals of the TiO ₂ phase and / or the TiO ₂ phase and to form the TiC phase in the titanium oxide compound which have increased conductivity compared to titanium dioxide.

In a further preferred embodiment of the method for treating a titanium oxide compound, the pressure in the gas atmosphere is atmospheric pressure. Compared to a treatment at a pressure which is higher than atmospheric pressure, this results in the advantage of a method which can be easily visualized in terms of apparatus. In a further preferred embodiment of the method of treating a titanium oxide compound, the titanium oxide compound is present as a titanium dioxide compound having a titanium dioxide content of at least 99.5 weight percent, based on the total weight of the titanium dioxide compound. Preferably, the titanium oxide compound is further in the form of titanium dioxide with anatase and / or rutile modification. In particular, the titanium oxide compound may be present as AEROXIDE TiO ₂ P25 (AEROXIDE is a registered trademark of Evonik Degussa GmbH). Preferably, the titanium oxide compound is further present as a powder, more preferably as a titanium dioxide powder and more preferably as a titanium dioxide powder having a titanium dioxide content of at least 99.5 weight percent, based on the total weight of the powder. It is further preferred that the powder be in the form of particles, particles or grains, preferably in the form of substantially spherical particles, particles or grains. The average particle size of the powder is preferably between 2 nm and 1000 nm. The mean particle size is preferably at most 100 nm, particularly preferably at most 50 nm, particularly preferably at most 25 nm. Most preferably, the average particle size is between 20 nm and 25 nm For example, the titanium oxide compound is preferably present in a minimum amount. The minimum amount is preferably 0.1 g, more preferably 1 g, more preferably 10 g and most preferably 100 g.

In the method according to the invention for treating a titanium oxide compound, the properties of the titanium oxide compound can be specifically changed by setting a suitable temperature, in particular the proportion of the elements carbon, nitrogen and / or hydrogen which occupy interstitial sites in the titanium oxide crystal lattice after treatment, replace oxygen atoms in the titanium oxide compound and / or in the crystal structure of the titanium oxide compound in titanium carbide structure and / or as mixed crystals of the TiO ₂ phase and / or the TiO ₂ phase and the TiC phase are embedded compared to the proportion of said elements, in the form of amorphous and / or crystalline inclusions are contained in the titanium oxide compound or are present as described above in addition to the titanium oxide in amorphous and / or crystalline form. In particular, as the temperature increases, the proportion of said elements which, in addition to the titanium oxide compound, is present in amorphous and / or crystalline form in addition to the titanium oxide compound, is not contained in the treated titanium oxide compound itself. The temperature is preferably at least 700 ° C, preferably at least 800 ° C, more preferably at least 900 ° C, further preferably 1000 ° C. However, it is preferable that the temperature is not higher than 1050 ° C in view of the above-mentioned increase in the proportion of said elements besides the titanium oxide compound besides the titanium oxide compound in amorphous and / or crystalline form. The period of time during which the temperature is applied can also be adjusted to change its properties. Preferably, the temperature treatment is carried out in a period of 5 min to 15 min, more preferably 8 min to 12 min, more preferably 9 min to 11 min, and most preferably for 10 min.

Process for producing a nanostructure of a titanium oxide compound

In a preferred embodiment of the method for producing a nanostructure, wherein the titanium oxide compound is exposed to at least carbon, nitrogen and / or hydrogen and the titanium oxide compound thus treated is dispersed in an alkaline solution, the titanium oxide compound is a titanium dioxide compound having a titanium dioxide content of at least 99.5% by weight , based on the total weight of the titanium dioxide compound. Preferably, the titanium oxide compound is further than Titanium dioxide with anatase and / or rutile modification before. In particular, the titanium oxide compound may be present as AEROXIDE TiO ₂ P25 (AEROXIDE is a registered trademark of Evonik Degussa GmbH). Preferably, further, both the titanium oxide compound and the treated titanium oxide compound is present as a powder, more preferably as a titanium dioxide powder. It is further preferred that the powder be in the form of particles, particles or grains, preferably in the form of substantially spherical particles, particles or grains. The average particle size of the powder is preferably between 2 nm and 1000 nm. The average particle size is preferably at most 100 nm, particularly preferably at most 50 nm, particularly preferably at most 25 nm. Most preferably, the average particle size is between 20 nm and 25 nm.

In a preferred embodiment of the method for producing a titanium oxide nanostructure, the alkaline solution is a NaOH solution. By using a NaOH solution, nanotubes or nanor rolls can be formed particularly efficiently. In addition, such synthesized nanotubes or nanorubes are susceptible to an ion exchange process as described below in which, as a result of the synthesis, sodium ions embedded in the tube or roller walls can be exchanged for protons. This allows the nanostructure to be set up for ionic conduction (i.e., as a proton conductor). The molarity of the NaOH solution can be further adjusted to affect the specific surface area of the nanotubes or nanor rolls. Particularly low and particularly high molarities result in a comparatively low specific surface area. A good result with respect to a large specific surface area can be achieved when using at least 8 molar and at most 12 molar NaOH solution, preferably at least 9 molar and at most 11 molar NaOH solution, and most preferably a 10 molar NaOH solution.

In a further preferred embodiment of the method for producing a titanium oxide nanostructure, the dispersion obtained by the dispersion is exposed to a temperature of at least 80 ° C. By setting a suitable temperature, the shape and / or the specific surface of the nanostructure can be adjusted. Preferably, nanostructures are in tube or roller form having a specific surface area of at least 300 m ² / g, preferably at least 340 m ² / g, and more preferably at least 380 m ² / g produced. A preferred temperature range for this purpose is a temperature between 95 ° C and 125 ° C, more preferably between 100 ° C and 120 ° C.

In a further preferred embodiment of the method for producing a nanostructure of a titanium oxide compound, the dispersion is exposed to the temperature of at least 80 ° C under laboratory conditions, i. the dispersion is not pressurized to the environment. As a result, the method can be carried out in a simple manner and without elaborate production devices, such as autoclaves.

In a further preferred embodiment of the method for producing a titanium oxide nanostructure, the method further comprises the above-mentioned ion exchange method. In this method, a precipitate is extracted from the dispersion obtained by the dispersion, and the extracted precipitate is dispersed in HCl solution. The precipitate contains, preferably almost exclusively nanostructures of the titanium oxide compound in the form of aligned thin films or films and / or nanotubes or nanor rolls. By dispersing the precipitate in HCl solution, ions embedded in the tube or roller walls due to the synthesis of the alkaline solution, for example sodium ions using the above-described NaOH solution, can be exchanged for protons. With the ion exchange method, it is possible, for example, to form in the nanostructure a titanium oxide phase having the composition H _2m Ti _n O _{2n + m} with 0 ≦ m ≦ 1 and 1 ≦ n ≦ 6. This composition can vary from nanostructure to nanostructure. As described above, the nanostructures treated by the ion exchange method have ionic conductivity, that is, the electrical conductivity of the nanostructures can be improved. Typical values for the so achievable electrical conductivity are at least 10 ^-3 S / cm compared to typically 10 ^-6 S / cm for tubular or roller-shaped nanostructures synthesized from a titanium oxide compound that is not at least carbon, nitrogen and / or hydrogen was suspended. Preferably, the HCl solution is a 0.1 molar solution. Preferably, the precipitate is extracted from the dispersion exposed to the temperature of at least 80 ° C. Further, the extracted precipitate is preferably dispersed at least once in the demineralized water and then filtered before being dispersed in HCl solution. Preferably, the dispersion in HCl solution is followed by a filtration, and the filtrate obtained is preferably at least once again dispersed in demineralized water and then filtered. Preferably, dispersing and filtering before dispersing in HCl solution and dispersing and filtering after dispersing in HCl solution are repeated until the respective filtrate has an electrical conductivity which is less than or equal to a predetermined first and second threshold, respectively wherein the first threshold is greater than the second threshold. The first threshold value is preferably 20 μS / cm and the second threshold value is 2 μS / cm.

In a further preferred embodiment of the method for producing a titanium oxide nanostructure, the period of time during which the temperature is applied to the dispersion is adjusted to adjust the specific surface area. Particularly large specific surfaces can be achieved if, in particular in the embodiments of the method described above, the temperature treatment takes place over a period of at least 15 h, preferably at least 20 h, particularly preferably at least 25 h.

In a further preferred embodiment of the method for producing a nanostructure of a titanium oxide compound, the solids content of the titanium oxide compound in the dispersion obtained by dispersing in the embodiments of the method described above is at least 0.1 g / l, preferably at least 0.25 g / l, more preferably at least 1 g / l, more preferably at least 2 g / l and, more preferably at least 2.5 g / l and most preferably at least 3 g / l.

A method for increasing the electrical conductivity of a nanostructure of a titanium oxide compound

In a preferred embodiment of the method for increasing the electrical conductivity of a titanium oxide nanostructure, the inert gas is N ₂ and the further gas is Ethingas. As described above in relation to the method for treating a titanium oxide compound, it is possible by using carbonaceous gases such as Ethingas, for example TiO _x C _y phases with 0 ≤ x <2 and 0 <y ≤ 0.05 and / or mixed crystals of the TiO ₂ phase and / or the TiO phase and the TiC phase in the titanium oxide compound, which have an increased conductivity compared to TiO ₂ .

In a further preferred embodiment of the method for increasing the electrical conductivity of a nanostructure of a titanium oxide compound, the volume fraction of the further gas in the gas atmosphere is at least 20% by volume, more preferably at least 30% by volume, more preferably at least 40% by volume and most preferably at least 50% by volume.

In a further preferred embodiment of the method for increasing the electrical conductivity of a nanostructure of a titanium oxide compound, the temperature to which the nanostructure is exposed is 300 ° C. or more in order to achieve embedding of carbon, nitrogen and / or hydrogen in the nanostructure. Preferably, the temperature is 350 ° C or more, more preferably 375 ° C or more, and most preferably 400 ° C or more. In this temperature range, for example, the above-mentioned TiO _x C _y phases or mixed crystals can be formed without the tube or roller shape of the nanostructure completely collapsing. Preferably, a temperature of 600 ° C or less, more preferably 500 ° C or less, and most preferably 425 ° C or less, is further provided for as little as possible to change the tube or roller shape of the nanostructure and its specific surface area. Particularly preferred in this regard with regard to the largest possible specific surface temperature range between 375 ° C and 400 ° C, most preferably between 380 ° C and 390 ° C, and with a view to the greatest possible electrical conductivity, a temperature range between 400 ° C and 425 ° C, more preferably between 410 ° C and 420 ° C. On the other hand, a comparatively high temperature can be used purposefully to produce a nanostructure in the form of a band. Preferably, a temperature of at least 450 ° C., preferably of at least 500 ° C., more preferably of at least 550 ° C., and very particularly preferably of at least 600 ° C. is used for this purpose. The nanostructure is preferably exposed to the temperature for at least 80 minutes, preferably at least 150 minutes, and particularly preferably at least 210 minutes, but preferably for a maximum of 300 minutes and particularly preferably for a maximum of 240 minutes.

It is also preferable to apply the described method for increasing the electrical conductivity to a nanostructure made of a titanium oxide compound using the method described above for producing a nanostructure to further increase its electrical conductivity.

Nanostructure of a titanium oxide compound with tube or roller form

In a preferred embodiment of the nanostructure of a titanium oxide compound having a tube or roller form and an electrical conductivity at room temperature of at least 10 ^-3 S / cm, the amount of carbon, nitrogen and / or hydrogen contained in the nanostructure is at least 4% by weight, based on the total mass of the nanostructure, preferably at least 6% by weight, more preferably at least 10% by weight, particularly preferably at least 15% by weight and most preferably at least 20% by weight. Further, it is preferred to indicate the amount of said elements alternatively in atomic percent. In this case, the nanostructure contains an amount of carbon, nitrogen and / or hydrogen amounting to at least 2 at%, based on the total number of atoms of the titanium oxide compound, preferably at least 5 at%, more preferably at least 10 at%, more preferably of at least 20 at% and most preferably at least 30 at%. Furthermore, the electrical conductivity is preferably at least 5 × 10 ^-3 S / cm, more preferably at least 10 ^-2 S / cm and most preferably at least 5 × 10 ^-2 S / cm.

In a further preferred embodiment of this nanostructure, the nanostructure has a specific surface area at room temperature of at least 175 m ² / g. The specific surface area is preferably at least 200 m ² / g, more preferably at least 250 m ² / g, more preferably at least 300 m ² / g, particularly preferably at least 340 m ² / g and most preferably at least 400 m ² / g. A large specific surface provides an advantageous, large reaction surface, for example, for a photocatalytic reaction which is possible due to the electrical conductivity given according to the invention.

In a preferred embodiment of the nanostructure of a titanium oxide compound having a tube or roller form and a specific surface at room temperature of at least 175 m ² / g, the amount of carbon, nitrogen and / or hydrogen contained in the nanostructure is at least 4% by weight, based on the Total mass of the nanostructure, preferably at least 6% by weight, more preferably at least 10% by weight, more preferably at least 15% by weight and most preferably at least 20% by weight. Further, it is preferred to indicate the amount of said elements alternatively in atomic percent. In this case, the nanostructure contains at least 2 at% of carbon, nitrogen and / or hydrogen, based on the total number of atoms of the titanium oxide compound, preferably of at least 5 at%, more preferably at least 10 at%, more preferably at least 20 at% and most preferably at least 30 at%. Furthermore, the specific surface area is preferably at least 200 m ² / g, more preferably at least 250 m ² / g, more preferably at least 300 m ² / g, particularly preferably at least 340 m ² / g and most preferably at least 400 m ² / g.

In a further preferred embodiment of this nanostructure, the nanostructure has an electrical conductivity of at least 10 ^-3 S / cm. The electrical conductivity is preferably at least 5 × 10 ^-3 S / cm, more preferably at least 10 ^-2 S / cm, and most preferably at least 5 × 10 ^-2 S / cm. A high electrical conductivity provides an advantageous, large number of photoinducible charge carriers (for example, electron-hole pairs), for example, for a photocatalytic reaction which is possible due to the intrinsic large specific surface of the nanostructure according to the invention.

In a further preferred embodiment of the tube or roller _-shaped nanostructures, the nanostructure contains a crystal structure which corresponds to that of a compound having the composition TiO _{2 -yx} R _x with 0 <x _≦ 0.05 and 0 ≦ y ≦ 1, where R is carbon Represents nitrogen or hydrogen. The nanostructure may be wholly or partially present in this crystal structure. The proportion of the atoms of the atomic species R present in this crystal structure relative to the total atomic number of the atomic species R in the nanostructure is preferably at least 1 at%, more preferably at least 5 at%, more preferably at least 10 at%, most preferably at least 20 at%, most particularly preferably at least 25 at%. This provides a particularly high electrical conductivity of the nanostructure compared to titanium dioxide. Preferably, the nanostructure contains at least two elements of carbon, nitrogen and hydrogen (codoping). As a result, the electrical conductivity can be increased particularly efficiently. Further, the nanostructure may further contain a phase of a titanium oxide compound having the composition H _2m Ti _n O _{2n + m} with 0 ≦ m ≦ 1 and 1 ≦ n ≦ 6, as achievable by the aforementioned ion exchange method. The nanostructure may consist entirely or partially of this phase.

In a further preferred embodiment of the nanostructures with tube or roller form, the nanostructure contains carbon, wherein the carbon contained is located on interstices and / or lattice sites of the nanostructure and / or in a titanium carbide and / or in the form of a mixed crystal of the TiO ₂ phase and / or the TiO phase and the TiC phase, ie one or more parts of the nanostructure are in a crystal structure corresponding to a titanium carbide crystal or said mixed crystal. This provides a particularly high electrical conductivity of the nanostructure compared to titanium dioxide.

In a further preferred embodiment of the tube or roller nanostructures, an outer diameter of the nanostructure is 3 nm or more. Preferably, the outer diameter is 100 nm or less. Preferably, the outer diameter of the nanostructure is at least 7 nm and at most 10 nm. Preferably, the inner diameter of the nanostructure is at least 5 nm and at most 7 nm. A length of the nanostructure is preferably at least 10 nm, preferably at least 50 nm, preferably at least 100 nm, more preferably at least 500 nm and most preferably at least 1 μm.

Nanostructure of a titanium oxide compound with ribbon shape

In a preferred embodiment of the band-shaped titanium oxide nanostructure, the nanostructure has a specific surface area between 5 m ² / g and 150 m ² / g, preferably between 50 m ² / g and 100 m ² / g.

In a further preferred embodiment of the band _-shaped nanostructure, the nanostructure contains a crystal structure which corresponds to that of a compound having the composition TiO _{2 -yx} R _x with 0 <x _≦ 0.05 and 0 ≦ y ≦ 1, where R is carbon, nitrogen or Represents hydrogen. The nanostructure may be wholly or partially present in this crystal structure. The proportion of the atoms of the atomic species R present in this crystal structure relative to the total atomic number of the atomic species R in the nanostructure is preferably at least 1 at%, more preferably at least 5 at%, more preferably at least 10 at%, most preferably at least 20 at%, most particularly preferably at least 25 at%. This provides a particularly high electrical conductivity of the nanostructure compared to TiO ₂ . Preferably, the nanostructure contains at least two elements of carbon, nitrogen and hydrogen (codoping). As a result, the electrical conductivity can be increased particularly efficiently. Furthermore, the nanostructure can also be a phase of a Titanium oxide compound having the composition H _2m Ti _n O _{2n + m} with 0 ≤ m ≤ 1 and 1 ≤ n ≤ 6 as achievable by the aforementioned ion exchange method. The nanostructure may consist entirely or partially of this phase.

In a further preferred embodiment of the band-shaped nanostructure, the nanostructure contains carbon, wherein the carbon contained is located on interstices and / or lattice sites of the nanostructure and / or in a titanium carbide structure and / or in the form of a mixed crystal of the TiO ₂ phase and / or TiO phase and the TiC phase is present, ie one or more parts of the nanostructure are present in a crystal structure corresponding to a titanium carbide crystal or said mixed crystal. This provides a particularly increased electrical conductivity of the nanostructure compared to TiO ₂ .

In a further preferred embodiment of the band-form nanostructure, a width of the nanostructure in a direction perpendicular to the band-stretching direction is 10 nm or more, preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 1000 nm or more , Preferably, the thickness of the nanostructure perpendicular to the band extension direction and perpendicular to the width direction of the nanostructure is 5 nm or more, preferably 10 nm or more, more preferably 100 nm and most preferably 1000 nm or more. A length of the nanostructure is preferably at least 10 nm, preferably at least 50 nm, preferably at least 100 nm, more preferably at least 500 nm and most preferably at least 1 μm.

In a further preferred embodiment of the tube, roll or ribbon nanostructure, the nanostructure is fabricated using one of the methods described above for producing a nanostructure and / or increasing the electrical conductivity of a nanostructure.

Brief description of the drawings

Further advantageous embodiments will be described in more detail below with reference to embodiments illustrated in the drawings, to which the invention is not limited.

The reference numbers in all claims have no limiting effect but are only intended to improve their readability.

Fig. 1

Eine Behandlungsvorrichtung zur Behandlung einer Titanoxidverbindung;

Fig. 2

eine Nanostruktursynthesevorrichtung;

Fig. 3

ein Diagramm, das den Ablauf des Ionenaustauschverfahrens illustriert;

Fig. 4

ein Diagramm, das spezifische Oberflächen und elektrische Leitfähigkeiten von Nanostrukturen aus Titanoxidverbindungen illustriert, die dem Verfahren zum Behandeln einer Titanoxidverbindung unterzogen wurden;

Fig. 5

ein Diagramm, das spezifische Oberflächen und elektrische Leitfähigkeiten von Nanostrukturen illustriert, die dem Verfahren zur Erhöhung der elektrischen Leitfähigkeit unterzogen wurden.

They show schematically:

Fig. 1

A treatment apparatus for treating a titanium oxide compound;

Fig. 2

a nanostructure synthesizer;

Fig. 3

a diagram illustrating the process of the ion exchange process;

Fig. 4

FIG. 3 is a graph illustrating specific surface areas and electrical conductivities of nanostructures of titanium oxide compounds that have been subjected to the process of treating a titanium oxide compound; FIG.

Fig. 5

a diagram illustrating specific surfaces and electrical conductivities of nanostructures, which have been subjected to the method for increasing the electrical conductivity.

Detailed description based on embodiments

In the following description of preferred embodiments of the present invention, like reference characters designate like or similar components.

The process according to the invention for treating a titanium oxide compound takes place in this embodiment by means of the in Fig. 1 shown treatment device, also called mini-reactor. The treatment device comprises an insulation housing 1 containing a refractory material 2. In the insulating housing 1, a ceramic tube 3 is arranged to be pulled out and sealed against the environment of the insulating housing with a refractory material (not shown). The ceramic tube 3 has an inner diameter of 6 mm in this embodiment. In the insulation housing 1, a heating device 4, for example, a high-temperature electrical heating, is also provided which includes the ceramic tube 3 with respect to the longitudinal direction partially and in its cross-section completely, the ceramic tube 3 is also arranged to be pulled out relative to the heater 4. The heater is over a control 5, for example an electrical supply line, controllable. In operation, a region 6 of the ceramic tube, which is surrounded by the heating device 4, forms a heating region, into which a sample 7, according to the invention a titanium oxide compound, can be introduced. In this embodiment, the heating region 6 in the longitudinal direction of the ceramic tube 3 has an extension of at least 30 mm. To monitor the temperature reached during operation in the heating device 4 and the temperature to which the sample 7 is exposed during operation, a heater temperature sensor 8 and a sample temperature sensor 9 are provided. The sample may be exposed via the gas supply 10 to a gas atmosphere under a predetermined pressure. For this purpose, the treatment device comprises a control device, not shown, with which a predetermined gas flow through the ceramic tube 3 can be controlled. The supplied gas is discharged via a gas outlet 11 to a wash bottle, not shown. For controlling the heating device 4 and the gas flow control device, a control unit, not shown, is provided, which is in operative connection with the gas flow control device and the heating device.

For the treatment according to the invention, a titanium oxide compound is introduced as sample 7 into the heating region 6. Sample 7 is exposed to a gas atmosphere and a temperature, for example as indicated in Table 1 below, by appropriate control of the heater 4 and the gas flow control device. In this case, a heating or cooling ramp is preferably set as indicated in Table 1 for reaching the target temperature. The titanium oxide compound in the cases shown in Table 1 is an AEROXID TiO ₂ P25 powder, available from EVONIK Industries AG, having a purity of 99.5% (weight percent TiO ₂ compared to the weight of the powder product). The gas atmosphere is preferably formed of Ethingas in the volume fraction of the gas atmosphere indicated in Table 1, and the remaining portion is preferably formed of the inert gas N ₂ . The designation CP0 designates a TiO ₂ P25 powder in the delivery condition. Table 1: Parameters for the carbothermal treatment of titanium dioxide powder treatment example Temperature [° C] Atmosphere [Vol.%] Gas flow [l / min] Holding time [min] Heating / cooling rate [K / min] CP0 - - - - CP7 700 10 (remainder: N ₂ ) 0.3 10 50/25 CP8 800 10 (remainder: N ₂ ) 0.3 10 50/25 CP9 900 10 (remainder: N ₂ ) 0.3 10 50/25 CP9,5 950 10 (remainder: N ₂ ) 0.3 10 50/25 CP10 1000 10 (remainder: N ₂ ) 0.3 10 50/25 CP10,5 1050 10 (remainder: N ₂ ) 0.3 10 50/25

Finally, the samples treated by this method are removed from the treatment device. The process exemplified above for treating a titanium oxide compound with a carbon-containing gas atmosphere is also referred to as a carbothermal process.

The inventive method for producing a nanostructure of a titanium oxide compound by means of in Fig. 2 shown synthesis device. The synthesis device comprises a bottle 21, for example a polytetrafluoroethylene bottle, which is held by a holding arm 22 and into which a hose 23, for example a silicone hose, is inserted. The tube 23 is passed through a stopper of a bottle cap 24. The bottle cap and the hose passage in the plug are sealed against the environment. Within the bottle 21, a stirring device 25, for example a magnetic stirrer, is arranged. The stirring device may be driven and controlled by a stirring device drive, not shown, such as a rotatable magnet.

The bottle is placed in an oil bath 26 which is located in a container 27. The container 27 is disposed on a heating plate 28 and thermally insulated from the environment of the container 27 with a container insulation 29. The heating plate 28, the container 27 including container insulation 29 and the bottle 21 together with the holding arm 22 and cover 24 is further surrounded by an outer insulation 30 and thereby thermally insulated from the environment. For measuring the oil bath temperature, a temperature sensor 31 is further provided, which protrudes into the container 27 and the oil bath temperature at two vertically spaced positions 31 a and 31 b measures. The temperature sensor 31 is connectable via a data line 33 with a control unit, not shown. The data line 33, the tube 23, a power supply not shown for the heating plate and also not shown supply and control line for the Rührvorrichtungsantrieb are guided by thermally insulated bushings through the outer insulation 30 to the outside.

For the preparation of the nanostructures in this embodiment, a titanium oxide compound, for example, the above-described AEROXID TiO ₂ P25 powder dispersed in demineralized water. Preferably, the dispersion is sonicated for 15 minutes. NaOH pellets (available from Carl Roth GmbH & Co. KG, purity ≥ 99%) are then added with stirring to the dispersion until a 10 molar NaOH solution is reached. This dispersion is introduced via the tube 23 into the bottle 21 and exposed in the reaction region 32 of the bottle 21 to a temperature which is controlled by the controller shown on the hot plate and based on the determined at the measuring positions 31 a and 31 b of the temperature sensor 31 temperatures. In this case, the bottle 21 is opened in this embodiment, for example via the hose 23 against the environment, so that the temperature treatment is carried out at atmospheric pressure or ambient pressure. The tube serves as a reflux condenser in the manner of a Dimroth cooler to condense evaporating water from the NaOH solution and returned to the bottle 21. As a result, the NaOH concentration during the temperature treatment does not change or only insignificantly. After completion of the temperature treatment, the dispersion of the bottle 21 is removed and filtered. The filtrate contains the nanostructures of the titanium oxide compound in nanotube or nanorollchenform.

In Table 2, synthesis parameters for producing nanotubes or nanorubes of titanium dioxide are given by the method described above. The titanium dioxide used in each case is an AEROXID TiO ₂ P25 powder in the delivery state. Table 2: Synthesis parameters for titanium dioxide nanostructures Synthesis Example Temperature [° C] Duration [h] Solids content [g / l] Concentration NaOH [mol / l] Volume NaOH [ml] SB1 100 25 0.25 10 400 SB2 100 25 2.50 10 400 SB3 100 25 4.75 10 400 SB4 120 25 0.25 10 400 SB5 120 25 2.50 10 400 SB6 120 25 4.75 10 400 SB7 100 20 2.50 10 400 SB8 100 25 2.50 10 400 SB 9 100 30 2.50 10 400 SB10 120 20 2.50 10 400 SB11 120 25 2.50 10 400 SB12 120 30 2.50 10 400

Sodium ions, which are incorporated by synthesis between the walls of the nanotubes or nanor rolls, are exchanged for protons by means of an ion exchange process following the synthesis described above. The procedure is schematic in Fig. 3 shown. For this purpose, the filtrate obtained in the synthesis (in step S1) is first dispersed in demineralized water (step S2) and then filtered (step S3). The steps S2 and S3 are repeated as many times (step S3a) until the filtrate has an electrical conductivity of at most 20 μS / cm. The filtrate thus obtained is then put into a 0.1 molar HCl solution (step S4) and stirred for a while, for example, for 5 minutes, 10 minutes or 15 minutes, and then filtered (step S5). The filtrate thus obtained is dispersed again in demineralized water (step S6) and then filtered (step S7). Steps S6 and S7 are repeated (S7a) until the resulting filtrate has an electrical conductivity of at most 2 μS / cm. Finally, the resulting filtrate is dried (step S8).

The above-described production method according to the present invention is also applicable to titanium oxide compounds treated by the above-described treatment method, for example, a carbothermally treated AEROXID TiO ₂ P25 powder. As exemplary synthesis parameters for the production of corresponding nanotubes or nanor rolls, parameters are selected which are particularly great for untreated titanium oxide compounds specific surfaces resulted. In this embodiment, these are a temperature of 115 ° C, a duration of 20 hours, a solids content between 2.5 g / l and 3 g / l, a NaOH concentration of 10 mol / l and a NaOH volume of 400 ml The exemplary nanostructures thus obtained are shown in Table 3. Table 3: Nanostructures of carbothermally treated titanium dioxide nanostructure starting material CSB1 CP7 CSB2 CP8 CSB3 CP9 CSB4 CP9,5 CSB5 CP10 CSB6 CP10,5 CSB0 CP0

Nanostructures of a titanium oxide compound, in particular nanostructures synthesized in the above-described preparation process, can be used according to the invention by means of the methods described in US Pat Fig. 1 treatment apparatus shown subjected to the inventive method for increasing the electrical conductivity of the nanostructures. In this method, in this exemplary embodiment, nanostructures such as nanotubes or nanorolls made of a titanium oxide compound are introduced into the heating region 6 of the treatment device and exposed to a gas atmosphere and to a temperature between 200 ° C. and 700 ° C. The gas atmosphere may be the gas atmosphere given in Table 1. Exemplary parameters for increasing conductivity by this method are given in Table 4. The nanostructures treated according to Table 4 are nanostructures synthesized with the parameters mentioned above in relation to Table 3, ie with a temperature of 115 ° C, a duration of 20 hours, a solids content between 2.5 g / l and 3 g / l, a NaOH concentration of 10 mol / l and a NaOH volume of 400 ml. Here, example NSB0 is an untreated reference example. Table 4: Post-treatment of nanostructures with the carbothermal process aftertreatment example Temperature [° C] Atmosphere [Vol.%] Gas flow [l / min] Holding time [min] Heating / cooling rate [K / min] NSB0 25 - - - - NSB1 350 30 0.3 60 10 NSB2 375 30 0.3 60 10 NSB3 400 30 0.3 60 10 NSB4 425 30 0.3 60 10 NSB5 350 50 0.3 60 10 NSB6 375 50 0.3 60 10 NSB7 400 50 0.3 60 10 NSB8 425 50 0.3 60 10

The following describes the properties of the titanium oxide compounds or the prepared and / or post-treated nanostructures treated by the above-described processes. The properties of the titanium oxide compounds and the nanostructures were determined using nitrogen adsorption according to the method of Brunauer, Emmett and Teller (BET), gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). examined.

The specific surface area of the nanostructures was determined by nitrogen adsorption on a NOVA 2200 instrument (Quantachrome, Boynton Beach, USA) according to the method of Brunauer, Emmett and Teller (BET). The nanostructures were baked at 150 ° C for 60 minutes in vacuo. The bath temperature was -195.75 ° C, the holding time 60 min (adsorption / desorption). All analyzes were performed on at least 300 mg nanostructures, which corresponds to about 10 ¹⁵ nanostructures per sample, to determine an average specific surface area based on a sufficiently large number of nanostructures.

For the thermogravimetric analysis (TGA), a thermogram TG Iris F1 (Netzsch Gerätebau, Selb, D) was used. All TGA analyzes were performed in an open Al ₂ O ₃ crucible with an assay sample mass of 10 to 20 mg of synthetic air. The gaseous decomposition products of TGA analysis were analyzed by coupled Tensor 27 FT-IR spectrometer (Bruker Optics, Billerica, USA).

Powder XRD analyzes were carried out on an X'Pert PRO diffractometer (PANalytical BV, Almelo, NL). For the evaluation of the diffraction reflexes the software X'Pert HighScore Plus (Version2.2d) and the reference database PAN-ICSD were used. The reflexes were adjusted by pseudo-Voigt fitting. The samples were backloaded and _analyzed using Cu K _α radiation (λ _Kα1 = 1.450598 A, λ _Kα2 = 1.544426 A, K _α1 / K _α2 = 0.5). The wavelength of the K _α1 radiation was used to calculate the interplanar spacings from the position of the peak maxima. The intensity and shift of the reflections were checked by means of external Al ₂ O ₃ and Si standards and required no further correction. Possible height errors were checked and excluded with the help of an internal standard. All samples were analyzed with the following settings: 2Θ start or end position: 5 ° - 100 °; irradiated length: 20 mm; Increment: 0.013 °; Time per step: 13.77 s; Tube voltage: 45 kV; Current: 40 mA.

The acceleration voltage of the elemental analysis by means of energy dispersive X-ray spectroscopy (EDX, EDAX Ametek), which took place at selected points of SEM samples, was typically 10 kV (analysis was based on Ti as the heaviest element).

Scanning electron micrographs were taken with a device of the LEO 1525 type (Carl Zeiss NTS GmbH, Oberkochen, D). The acceleration voltage was 5 kV, the working distance 5 mm. All samples were adhered to a double sided carbon pad and sputtered with spectral carbon.

Images taken on a CM300 transmission electron microscope (Philips N.V., Amsterdam, NL) were made with an acceleration voltage of 300 kV in bright-field mode. The samples were prepared on a copper grid with Lacy carbon film. For this purpose, the nanotube powders were dispersed in ethanol by means of ultrasound and applied to the carrier mesh.

The determination of the electrical conductivity was carried out by determining the electrical resistance of cylinders pressed in an Al ₂ O ₃ tube. For this purpose, the respective sample was filled into the tube by means of a funnel and to 0.4 g / cm ³ for Titanium oxide compounds and compressed to zw. 0.2 g / cm ³ for nanostructure samples using a manual screw press. The electrical conductivity was calculated from the measured resistance of the compacted sample, the measured length of the compacted sample and the pipe diameter.

With the analysis methods described above, the carbothermally treated titanium oxide compounds shown in Table 1 and the nanostructures shown in Tables 3 and 4 were examined. Random investigations with SEM and TEM showed that tubular or roller-shaped nanostructures with a wall thickness of 2 nm to 5 nm could be produced, which have lengths up to several μm. By means of SEM and TEM it was found that at sufficiently high after-treatment temperatures above 400 ° C. in Table 4, nanostructures with ribbon shape with a width of 39 nm to 45 nm, a thickness of at least 5 nm and lengths up to several μm can be produced.

Table 5 shows the proportion of carbon atoms, determined by gravimetric analysis, of the carbothermally treated titanium oxide compounds according to Table 1, based on the total number of atoms contained in the carbothermally treated titanium oxide compounds, and of the atoms present in crystalline and / or possibly present next to the carbothermally treated titanium oxide compounds. or amorphous carbon particles and / or crystalline and / or amorphous carbon coatings. Similarly, Table 6 shows the corresponding proportion of carbon atoms with respect to nanostructures prepared from the carbothermally treated titanium oxide compounds shown in Table 3. Table 5: Carbon content for carbothermally treated titanium dioxide according to Table 1 treatment example Temperature [° C] Carbon content [at%] Carbon content [% by weight] CP0 - - - CP7 700 41.9 24.5 CP8 800 47.8 29.2 CP9 900 61.9 42.3 CP9,5 950 63.6 44.0 CP10 1000 58.4 38.7 CP10,5 1050 63.8 44.3 nanostructure starting material Carbon content [at%] Carbon content [% by weight] CSB0 CP0 - - CSB1 CP7 10.3 6.0 CSB2 CP8 32.1 20.9 CSB3 CP9 50.9 36.7 CSB4 CP9,5 54.7 40.3 CSB5 CP10 57.5 43.1 CSB6 CP10,5 58.0 43.5

It can be seen from Tables 5 and 6 that, in particular, nanostructures CSB1 and CSB2 have a significantly reduced carbon content in comparison to the respective starting material CP7 and CP8. Without restricting itself to a particular theory, it is assumed here that part of the carbon to which the titanium oxide compound is exposed in the case of the thermal treatment is introduced into the titanium oxide compound by the carbothermal treatment and is therefore located on interstices and / or lattice sites of the titanium oxide compound and / or a titanium carbide structure and / or in the form of a mixed crystal of the TiO ₂ phase and / or the TiO ₂ phase and the TiC phase in the titanium oxide compound. It is further believed that another portion of the carbon provided is in addition to the titanium oxide compound in amorphous and / or crystalline form, eg as carbon particles and / or as a carbon coating of the titanium oxide compound. In the production of nanostructures from the carbothermally treated titanium oxide compounds, the former part remains during and after the nanostructural synthesis at the sites described or in the form described. In contrast, the latter part is washed out or filtered out during nanostructural synthesis, so that the nanostructures produced have a reduced carbon content in comparison to the corresponding carbothermally treated starting materials. That is, the values shown in Table 6 essentially indicate the proportion of carbon contained in the nanostructures, consistent with a review of the carbon content obtained by gravimetric analysis in Table 6 with elemental analysis of randomly selected nanostructures by EDX.

FIG. 4 Figure 11 shows specific surface areas and electrical conductivities of nanostructures synthesized according to Table 3 from carbothermally treated titanium oxide compounds. The FIG. 4 shows that the nanostructure CSB0 synthesized from the untreated titanium oxide compound CP0 has conductivity several orders of magnitude lower than nanostructures such as CSB1 synthesized from the at least 700 ° C. treated carbothermal process such as CP7. Without being limited to a particular theory, it is assumed here that the increased conductivity is based on the fact that the carbon introduced into the titanium oxide compound by the carbothermal treatment as described above is also located on interstitial sites and / or lattice sites of the titanium oxide compound after nanostructural synthesis and or in a titanium carbide structure and / or in the form of a mixed crystal of the TiO ₂ phase and / or the TiO ₂ phase and the TiC phase in the nanostructure. In accordance with this assumption, XRD spectra of the carbothermally treated titanium oxide compounds have structures which do not exist in the untreated titanium oxide compound CP0 and indicate carbon contained in the titanium oxide compounds. For example, the spectra have a comparatively sharp maximum at 2θ~42 ° to 43 °, absent in the untreated titanium oxide compound CP0, indicating a TiO _x C _y type crystal structure. FIG. 4 also shows that as the temperature of the carbothermal treatment increases, the specific surface area of the nanostructures decreases, while the electrical conductivity increases up to a treatment temperature of 900 ° C, but remains substantially constant above this treatment temperature. A preferred temperature range for the carbothermal treatment with respect to the largest possible specific surface at the same time high electrical conductivity is therefore a range between 700 ° C and 900 ° C.

FIG. 5 Figure 4 shows specific surface areas and electrical conductivities of nanostructures treated according to Table 4 according to the conductivity enhancement method described above. The figure shows that in a temperature window around 400 ° C. it is possible to obtain nanostructures with significantly increased conductivity compared to the untreated nanostructure NSB0, while their specific surface area is not too reduced compared to the nanostructure NSB0, ie the tube or roller shape of the nanostructures is largely preserved. At the same time shows FIG. 5 that it is possible at temperatures well above 400 ° C nanostructures with further increased electrical conductivity and at the same time significantly reduced specific surface area, ie those whose tube or roller shape has collapsed to a band-shaped nanostructure.

The features disclosed in the foregoing description, claims and drawings may be significant to the realization of the invention in its various forms both individually and in any combination thereof.

LIST OF REFERENCE NUMBERS

1

insulating housing

2

refractory material

3

ceramic tube

4

heater

5

control

6

heating

7

sample

8th

Heizvorrichtungstemperaturfühler

9

Sample temperature sensor

10

gas supply

11

gas outlet

21

bottle

22

holding arm

23

tube

24

bottle caps

25

stirrer

26

oil bath

27

container

28

heating plate

29

tank insulation

30

external insulation

31

temperature sensor

31a, 31b

Temperature measurement positions

32

reaction region

33

data line

Claims (15)

A method of treating a titanium oxide compound, wherein the titanium oxide compound is exposed to at least one of carbon, nitrogen and / or hydrogen and a temperature between 600 ° C and 1200 ° C. A method according to claim 1, wherein the titanium oxide compound is exposed to a gas atmosphere containing at least carbon, nitrogen and / or hydrogen, preferably at a temperature between 600 ° C and 1200 ° C, preferably wherein the pressure in the gas atmosphere is atmospheric pressure. A method according to claim 2, characterized in that the gas atmosphere contains an inert gas and another, at least carbon, nitrogen and / or hydrogen-containing gas, and wherein preferably the volume fraction of the further gas to the gas atmosphere is at least 10 percent by volume and wherein preferably the inert gas N ₂ and the more gas is Ethingas. Method according to one of the preceding claims, characterized in that the titanium oxide compound is present as a powder, preferably as titanium dioxide powder, and particularly preferably as titanium dioxide powder having a titanium dioxide content of at least 99.5 weight percent, based on the total weight of the titanium dioxide compound. A method of producing a nanostructure of a titanium oxide compound, wherein a titanium oxide compound is treated by the method of any of claims 1 to 4, and the titanium oxide compound thus treated is dispersed in an alkaline solution. A method of producing a nanostructure of a titanium oxide compound, wherein the titanium oxide compound is exposed to at least carbon, nitrogen and / or hydrogen, and the thus-treated titanium oxide compound is dispersed in an alkaline solution. A method according to claim 5 or 6, characterized in that the alkaline solution is a NaOH solution, preferably an at least 8 molar NaOH solution, and more preferably an at least 10 molar NaOH solution. Method according to one of claims 5 to 7, characterized in that the dispersion obtained by the dispersion is exposed to a temperature of at least 80 ° C. A method according to any one of claims 5 to 8, characterized in that a precipitate is extracted from the dispersion obtained by dispersing, and the extracted precipitate is dispersed in HCl solution. A method for increasing the electrical conductivity of a nanostructure of a titanium oxide compound, wherein the nanostructure of a gas atmosphere and a temperature between 200 ° C and 700 ° C is exposed, wherein the gas atmosphere, an inert gas and another, at least carbon, nitrogen and / or hydrogen-containing gas contains, and wherein the volume fraction of the further gas in the gas atmosphere is at least 10 percent by volume. A method according to claim 10, characterized in that the nanostructure is produced by a method according to one of claims 5 to 9. The nanostructure of a titanium oxide compound, characterized in that the nanostructure comprises a tube or roll form, contains at least one of carbon, nitrogen and / or hydrogen, wherein the amount of carbon, nitrogen and / or hydrogen, at least 2 wt%, based on the total mass of the nanostructure , is, and has an electrical conductivity at room temperature of at least 10 ^-3 S / cm, wherein the nanostructure preferably has a specific surface area at room temperature of at least 175 m ² / g. Nanostructure of a titanium oxide compound, characterized in that the nanostructure has a tube or roller form containing at least carbon, nitrogen and / or hydrogen, wherein the amount of carbon, nitrogen and / or hydrogen at least 2% by weight, based on the total number of atoms the nanostructure is, and a specific surface at Room temperature of at least 175 m ² / g, wherein the nanostructure preferably has an electrical conductivity at room temperature of at least 10 ^-3 S / cm. Nanostructure according to claim 12 or 13, characterized in that the nanostructure is produced using the method according to one of claims 5 to 11. Nanostructure of a titanium oxide compound, characterized in that the nanostructure has a band shape, at least carbon, nitrogen and / or hydrogen, wherein the amount of carbon, nitrogen and / or hydrogen is at least 2% by weight, based on the total mass of the nanostructure, and has an electrical conductivity at room temperature of at least 10 ^-3 S / cm.

Images